Cut Halo 3 levels
From Halopedia, the Halo wiki
During the development of Halo 3, a number of levels were cut or changed dramatically.
Cut campaign levels
Guardian Forest was a cut level set either between The Ark and The Covenant or after The Covenant but before Cortana. The level was set in a large forest on Installation 00 and was to feature a new enemy, the Guardian.
Early campaign levels
An early version of Cortana was supposed to feature more High Charity specific geometry but this was cut. Instead parts of the level Floodgate was split a part with some of that geometry becoming the Cortana that was released.
Development and testing levels
The Lost City
The Lost City was a visual look-development level. The level was based around the idea of a Forerunner city, composed of a single building. The space had grown immense in size. An art pass was done on the level in 2005 before it was cut.